I have just received my new Explore Scientific 3" 30mm 100 degree eyepiece. In general the build quality appears excellent. The coatings look good out of the box and the field stop is actually smaller than I thought it would be. It should be possible to provide an even wider field than 100 degrees at 30mm. The small round green "Ar" sticker on the eyepiece body is peeling slightly but generally the eyepiece appears well built. At around 5 pounds it certainly has weight and heft, but not overwhelmingly so. The weight is not an issue for my rig as my AP1600GTO can easily handle the weight distribution. Below is a comparative picture of the ES 3" 30mm with some other BIG eyepieces to give a sense of its size.

Unfortunately, I cannot write a first light report yet because of what appears a very serious flaw with the Explore Scientific 3" diagonal that I ordered with the eyepiece. As both arrived before I had a chance to make up a 3" adapter for my 180mm F/7 refractor, I improvised by attaching an Optec 3" focuser to receive the nosepiece of the ES 3" diagonal.

When I inserted the eyepiece and diagonal nosepiece into the 3" focuser and tightened the three set screws, the rest of the diagonal and eyepiece (c. 7 pounds of weight) suddenly rotated sidewards and literally fell off the nosepiece! If I had not reacted quickly enough to catch the eyepiece and rest of the diagonal, it would have dropped to the hard surface of my patio. (Or crushed my foot)

Upon inspection, the threads on the diagonal nosepiece are barely engaged with the rest of the diagonal main body making it impossible to tighten it. I originally thought that the nosepiece might have been overtightened at the factory, stripping the threads, but that does not appear the case. It just seems a poor fit and poor quality control. Currently the nosepiece freely rotates within the diagonal main body and cannot be tightened or used.

This serious flaw aside, my general impression is that the ES 3" diagonal is somewhat underbuilt for the weight and loading it needs to deal with. Just the torque of the weight of 5 pounds of eyepiece, if placed at an angle is going to place considerable strain on the way the nosepiece is threaded into the diagonal main body. Even on a properly threaded version, there is always the risk of it rotating sidewards. I think it needs to be secured along the lines of the diagonal eyepiece holder which has 6 hex heads securing it to a flange on the the main diagonal body. (Pictures in posts below)

One other point. I get that carbon-fibre inserts appear attractive from a marketing POV and superficially promise minor weight savings, but in reality anyone seriously using eyepieces in this weight category is not going to worry about a few ounces of extra weight for solid metal. From an engineering perspective, the thickness of the metal used in the diagonal is on the thin side, and the carbon fibre inserts make an already flimsy diagonal feel flimsier still.

I really wanted this post to be a positive first light review of the ES 30mm 3" eyepiece through a large apochromatic refractor and I still hope to write one soon, but the weak link in the chain represented by the diagonal needs to be resolved. Perhaps I received a poor early example, and I can go back to Opt to see if they will exchange it for another one. However I am also wondering whether I should look at the Siebert 3" diagonals or any other alternatives someone can recommend. (If anyone has any experience?)

Chris

Attached Files

Here is the 3" diagonal. You can see that the eyepiece outlet holder is well secured with 6 hex head bolts. The nosepiece inlet however is only screwed in and the threads do not properly engage in my example.

Attached Files

Hmm.. you appear to be assuming this eyepiece is being used in the 24" F/3.25 Newtonian listed in my signature which is the very last telescope I would use it in. Besides the weight and 3" focuser requirement, not the least is the unusable 9.24mm exit pupil.

This eyepiece is more suited to large 7"+ refractors and longer focal length cassegrains. The issues I had with the diagonal stem from attempting a preliminary test in my F/7 180mm refractor on an AP1600 equatorial mount. This combination yields a 2.381 degree true FOV at 42X with a 4.29mm exit pupil, versus a 2.024 true FOV at 41X in a 31mm TYpe 5 Nagler 31mm. Not a massive difference, but still significant from my perspective, and I like the aesthetics of the expansive wide field refractor view. I also have other longer focal length cassegrain telescopes to experiment with what this eyepiece can do.

It's a 52.2mm field stop versus a 42mm field stop on the 31 Nagler.That's a 24.3% wider true field.It should be, in the 1260mm FL 180mm refractor focal length, a difference of2.37 degrees versus 1.91 degrees. That's a fairly large difference, actually.

If a local machine shop can't make you an insertion tube that fits the diagonal tighter (install with loctite, too!), and I'd make it a thicker wall, try a "permanent" filler on the insertion tube threads, like JB Weld (if it's very loose), or Goodyear Pliobond (if it's just a trace loose). You can still clean the diagonal by removing the mirror.

Then if you tip the diagonal, keep it a small tilt, and ALWAYS tip to the right, never the left.

I think coarse, deep, threads would have been stronger, but it would take some machine work to get there.

Here is the 3" diagonal. You can see that the eyepiece outlet holder is well secured with 6 hex head bolts. The nosepiece inlet however is only screwed in and the threads do not properly engage in my example.

That does not look good.. I imagine ES will be working on a solution here shortly. To my eye as a mechanical engineer type, I would like to see more metal, it's too thin. This would be an ideal application for a one piece billet like the TV Everbright.

I am sorry this happened. My barrel seems fixed to the diagonal for now, but I am afraid to apply significant torque to it to find out. Please let us know after you call ES. Also, can you see if your 3"-2" adapter fits 2" eyepieces? If not, then there may be an issue with multiple samples of this diagonal.

If a local machine shop can't make you an insertion tube that fits the diagonal tighter (install with loctite, too!), and I'd make it a thicker wall, try a "permanent" filler on the insertion tube threads, like JB Weld (if it's very loose), or Goodyear Pliobond (if it's just a trace loose). You can still clean the diagonal by removing the mirror.

This is really an issue that Explore Scientific needs to address.

I thought about epoxy, it would probably work but epoxy is relatively brittle and there is not a lot of surface here, if it does fail, the entire conglomeration could hit the ground.. not a desirable scenario.

As far as machining a new adapter, that would represent a significant expense and it is likely that the threads on the diagonal body are damaged or improperly machined so a machinist would probably want to machine the diagonal body as well..

I am sorry this happened. My barrel seems fixed to the diagonal for now, but I am afraid to apply significant torque to it to find out. Please let us know after you call ES. Also, can you see if your 3"-2" adapter fits 2" eyepieces? If not, then there may be an issue with multiple samples of this diagonal.

Derek

Hi Derek, I had not even tried sliding a 2" eyepiece into the 3"-2" adapter so of course tried this morning. Uhhhh, you are right! The 2" opening of the adapter is extremely tight. I could force (literally) some 2" eyepieces in, but the undercuts made it a real bear to get them back out again. I also tried to insert an Astro-Physics 2" to 1.25" adapter but I could not get that to fit at all, no matter how hard I pushed.

Your nervousness about rotating the diagonal at an angle to view through the eyepiece comfortably, (as is quite reasonable for objects lower down) highlights the greater importance of engineering the diagonal properly with eyepieces in this weight class. In fact the larger telescopes suited to this eyepiece are, by definition, going to be higher off the ground, and limiting (as Don suggests) the eyepiece to a small tilt, is unreasonably cumbersome from a use-case perspective. A more solidly engineered diagonal would eliminate that concern.

I am getting a sense that the way such a large eyepiece is actually used has not been properly thought through, and the ES 3" diagonal appears to have been sloppily executed, perhaps as an afterthought to the eyepiece. The 2" adapter issue is frankly incredible for a manufacturer of this experience. Thats the risk of early adoption of course, and hopefully ES will look at basic design and manufacturing quality quickly.

Tonight, I should see if I can test the eyepiece straight through without the unusable diagonal, I would have done so last night, but fireworks and hotdogs took priority.

(BTW: Apologies, I did not see your parallel thread when posting and did not mean to duplicate. Perhaps keep this thread on 3" diagonal issues and the thread you initiated on the actual eyepiece itself and observing reports)

This is not entirely surprising. Most of the largest 2" eyepieces weigh about 2.2 pounds. Jumping to a 3" 5 pound eyepiece while using the same basic structural designs on a larger scale might uncover some problems. Now the mechanical engineers need to come up with solutions.

If the adapter issue is widespread, that is a small problem. If it is the entire diagonal then they will have a big issue. I plan on contacting them after I hear what the resolution is for your particular sample.

Actually, ES has contacted me personally over the weekend expressing their concern. That speaks highly about their sense of customer care. I am satisfied as being an early adopter of low volume speciality items like this carries with it risks that I accept.

Meanwhile, I have posted a short first light review on the parallel thread that Derek Wong initiated.

I wouldn't rely on any nose thread, no matter how well done to secure that weight. Specially because I naturally want to use the diagonal rotated to the side. I would put glue on the thread to make it permanently fixed.The three screws of the FT3545 are enough to hold it secure.

I have also been contacted by ES and they are going to examine the entire diagonal. They seem very concerned on fixing things the right way, and I am happy with their rapid (holiday weekend!) customer service so far.

But hey, it's your choice to validate a little bit more field plus a boatload of cash in exchange for 7.5 Lbs and a system that isn't happening !!!

Cheers! I hope it works out for you.

2.38 vs. 2.01 is a HUGE difference in field area; equivalent in field area difference to the surface area difference between a 20" and a 24" mirror! 44% more field of view area. That's absolutely massive in difference.